Cyclic flexing salt-spray chamber and methods

ABSTRACT

Aspects described herein generally relate to apparatus and methods for determining operational performance of material systems. Apparatus generally comprise a salt fog chamber having a fixture support having material system flexing components to test corrosion of an aircraft material system. In one aspect, a material performance chamber comprises a salt fog chamber and a jaw configured to flex a material system. Methods for determining corrosion include exposing a material system, such as a panel, to salt fog and flexing the material system at a frequency. In one aspect, a method for determining corrosion includes exposing a material system to a salt fog. The pH of the salt fog is from about 3.0 to about 9.0 and flexing the material system at a frequency from about 0.1 Hz to about 60 Hz.

FIELD

Aspects described herein generally relate to apparatus and methods fordetermining operational performance of material systems.

BACKGROUND

Spanning the lifetime of operation, an aircraft will experience repeatedand harsh conditions resulting in degradation of component parts of theaircraft. Such degradation may take the form of, for example, corrosionand subsequent metal fatigue and fracture. Corrosion can contribute to adecrease in the integrity and strength of aircraft components. Morespecifically, a material system comprising aircraft components, such asfuselage or skin panels, a coated lap joint between two metal panels, ora wing-to-fuselage assembly on the exterior of an aircraft, may corrodeover time due to exposure to mechanical and chemical stresses during useof the aircraft. Before a material is determined to be suitable for useas an aircraft material system, it may be desirable to determine thematerial system's propensity to corrode. However, performance ofaircraft material systems, such as panels, during actual, real world useof the aircraft seldom correlates with corrosion testing data.Furthermore, corrosion tests often lack consistency between tests. Forexample, variability is observed when similar material systems arecorroded in different testing apparatuses even though the testingconditions are nominally similar. Material system corrosion duringactual use versus corrosion experienced during testing is particularlydisparate when the material system comprises alloys or the materialsystem has surface finishes, primers or top coats applied to thematerial system. Furthermore, conventional processes for testingcorrosion are not effective at controlling the environment at anyparticular site on or within a test material system.

Therefore, there is a need in the art for methods and apparatus withcontrolled exposure environments for determining operationalenvironment-specific performance, lifetime assessment, and failure modeinvestigation, i.e. an exposure environment that more closely mimics theconditions a material system will experience when incorporated as acomponent of an aircraft during actual, real-world use.

SUMMARY

Aspects described herein generally relate to methods and apparatus fordetermining operational environment-specific performance, lifetimeassessment, and failure mode investigation of material systems.

In one aspect, a method for determining material performance includesexposing a material system to salt fog. The method further includesflexing the material system.

In another aspect, a method for determining material performanceincludes exposing a material system to a salt fog wherein the pH of thesalt fog ranges from about 3.0 to about 9.0. The method further includesflexing the material system at a frequency from about 0.1 Hz to about 60Hz.

In another aspect, a material performance chamber comprises a salt fogchamber and a jaw configured to flex a material system.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toaspects, some of which are illustrated in the appended drawings. It isto be noted, however, that the appended drawings illustrate only typicalaspects of this present disclosure and are therefore not to beconsidered limiting of its scope, for the present disclosure may admitto other equally effective aspects.

FIG. 1 is a plan view of an apparatus for accelerating and controllingthe corrosion-related failure modes of a material system, according toan aspect of the disclosure.

FIG. 2 is a side perspective view of an apparatus for accelerating andcontrolling the corrosion-related failure modes of a material system,according to an aspect of the disclosure.

FIG. 3 is a plan view of an apparatus for accelerating and controllingthe corrosion-related failure modes of a material system, according toan aspect of the disclosure.

FIG. 4 is a perspective view of a flexer configured to perform cyclicflexing, according to an aspect of the disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of one aspectmay be beneficially incorporated in other aspects without furtherrecitation.

DETAILED DESCRIPTION

The descriptions of the various aspects of the present disclosure havebeen presented for purposes of illustration, but are not intended to beexhaustive or limited to the aspects disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the described aspects.The terminology used herein was chosen to best explain the principles ofthe aspects, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the aspects disclosed herein.

Aspects described herein generally relate to apparatus and methods fordetermining operational performance of material systems. For example,determining operational environment-specific performance, lifetimeassessment, and failure mode investigation of material systems may beaccomplished by aspects described herein. Apparatus generally comprise asalt fog chamber comprising material system flexing components to moreaccurately test corrosion of an aircraft material system such as apanel, a coated lap joint between two metal panels, and awing-to-fuselage assembly. In one aspect, a corrosion chamber comprisesan enclosure, a fog nozzle, a liquid reservoir, and a fixture supportfor gripping and flexing a material system. Methods for determiningcorrosion include exposing a material system to salt fog and flexing thematerial system at a frequency. In one aspect, a method for determiningcorrosion includes exposing a material system to a salt fog for aduration of about 1 hour to about 4500 hours wherein the pH of the saltfog is from about 3.0 to about 9.0 and flexing the panel at a frequencyfrom about 0.1 Hz to about 60 Hz.

FIG. 1 is a plan view of an apparatus 100 for accelerating andcontrolling the corrosion-related failure modes of a material system,according to an aspect of the disclosure. FIG. 2 is a side perspectiveview of apparatus 100 of FIG. 1. One or more components of apparatus 100are made from materials that show resistance to a corrosive environment,such as an environment containing a salt fog. As shown in FIGS. 1 and 2,apparatus 100 includes an enclosure 160 having one or more fog nozzles102 (one shown) disposed therein and configured to spray a treatingliquid, such as a salt fog, in the enclosure 160. A fixture support isdisposed in the enclosure to support a material system for exposure andflexing therein. Apparatus 100 includes a liquid reservoir 104 to supplya treating liquid to fog nozzle 102. Fog nozzle 102 may be a nozzle,such as an atomizing nozzle, a nozzle calibrated for air consumption,BETE full cone nozzle, hollow cone nozzle, fan misting nozzle, tankwashing spray nozzle, NASA Mod1 nozzle for water spray atomization anddroplet control, Q-Lab OEM fogging nozzle, Cool Clean ChilAire Litespray applicator nozzle, and combinations thereof. Fog nozzle 102 may becomprised of materials such as hard rubber, plastic, or other inertmaterials.

The fixture support comprises jaws 124 a-e configured to flex a materialsystem. Plate 146 is configured to support jaws 124 a-e. In someaspects, plate 146 comprises a mounting plate disposed on an I-Beamgrate. Plate 146 is positioned between fog nozzle 102 and jaws 124 a-124e (as shown in FIGS. 1 and 2), allowing treating liquid to enter theenclosure without directly impinging upon a material system held by oneor more jaws 124 a-e. This configuration mimics general humidatmospheric conditions, as compared to direct rainfall onto an aircraftmaterial system. Alternatively, jaws 124 a-e may be positioned betweenfog nozzle 102 and plate 146 (this configuration not shown), allowingdirect flow of treating liquid toward a material system held by one ormore jaws 124 a-e. This configuration mimics direct rain fall or aerosoldeposition onto an aircraft material system. Fog nozzle 102 may beconfigured for flow angle adjustment, allowing flow of treating liquidat one or more angles relative to a material system surface. In someaspects, a material system surface may be parallel to a principaldirection of flow of liquid through apparatus 100, based upon thedominant surface being tested, which reduces liquid collection on amaterial system during corrosion testing performed in apparatus 100. Insuch aspects, fog nozzle 102 may be directed or baffled so that theliquid does not impinge directly on a material system. (Fog nozzle 102,a vent 122, a motor 126, an outer enclosure 136, and legs 148 a-f areshown as dashed lines in FIG. 1 to indicate that these parts are locatedbehind a plate 146 in the aspect shown in FIG. 1).

A fog pump 108 is configured to assist flow of a liquid from liquidreservoir 104 to fog nozzle 102 via first fluid line 106 and secondfluid line 110. First fluid line 106 couples liquid reservoir 104 at afirst end with fog pump 108 at a second end to provide liquidcommunication of liquid reservoir 104 with fog pump 108. Second fluidline 110 couples fog pump 108 at a first end with fog nozzle 102 at asecond end to provide liquid communication of fog pump 108 with fognozzle 102.

A compressed air source 112 and bubble tower 114 are configured toprovide humidified air to fog nozzle 102. In some aspects, a pressure inthe enclosure may be regulated to mimic the pressure experienced by anaircraft at various altitudes during real world use. Accordingly,compressed air source 112 is configured to flow air at a pressureranging from about 2 PSI to about 50 PSI, from about 5 PSI to about 30PSI, from about 12 PSI to about 18 PSI. In these ranges, lower pressurevalues mimic pressures experienced by an aircraft at higher altitudeswhile higher pressure values mimic pressures experienced by an aircraftat lower altitudes and closer to sea level. Air may include a mixture ofgases similar to that found in an ambient atmosphere, for example,comprising about 78% N₂, about 21% O₂, and about 0.039% CO₂, among othergases. Third fluid line 116 couples bubble tower 114 at a first end withfog nozzle 102 at a second end to provide air and liquid communicationof bubble tower 114 with fog nozzle 102. A compressed air line 118couples compressed air source 112 at a first end with bubble tower 114at a second end to provide air communication of compressed air source112 with bubble tower 114. Bubble tower 114 may contain a liquid, suchas water, to provide initial humidification or additional humidificationto air flowed from compressed air source 112 via compressed air line118.

A vent 122 may be coupled with the first chamber wall 130, a secondchamber wall 132, or a third wall 152 (FIG. 2) to provide pressureregulation inside of apparatus 100. A heater 120 may be provided andconfigured to heat the inside of apparatus 100 such as enclosure 160.Heater 120 may be disposed adjacent to a first wall 130 of apparatus 100and coupled with third wall 152 (FIG. 2). Heater 120 may be adhered tothird wall 152 using by any suitable adherent, such as rivets. Heater120 may be coupled with and controlled by controller 138.

Fixture support is configured to support and flex a material systempositioned in the enclosure for testing. Jaws 124 a, 124 b, 124 c, 124d, and 124 e are configured to flex a material system, such as a panel,a coated lap joint between two metal panels, a wing-to-fuselageassembly, and combinations thereof. The material system may be anaircraft material system, such as a panel, such as a skin or fuselageflat panel. The material system may have a width that is, for example,about 4 inches, and a length that is for example, about 6 inches toabout 14.5 inches. The fixture support may flex a material system to astrain ranging from about 0.05% to about 50%, about 0.1% to about 30%,about 0.3% to about 5%, such as about 0.37%.

Fixture support comprising one or more jaws 124 a-e is configured togrip and release a material system. Jaws 124 a-e are configured to flexa material system from a first starting position to a fully or partiallyflexed second position. Jaws 124 a-e are configured to flex a materialsystem from a first position to greater than 0° to about 180° from thestarting position, such as about 5° to about 90°, such as about 5° toabout 45°, during a flexing process. Jaws 124 a-124 e may be the samesize or different sizes. For example, jaw 124 a may be the same size asjaw 124 b, but be a different size than jaw 124 d (as shown in FIG. 1).Furthermore, jaws 124 a-124 e may be positioned from one another by adistance that is the same or different than a distance between adifferent pair of jaws 124 a-e. For example, a first distance betweenjaw 124 a and 124 b may be different than a second distance between jaw124 d and 124 e. Various jaw sizes and various distances between jawsallow, for example, simultaneous testing of different sized materialsystems, such as panels, during an exposing and flexing process withinapparatus 100. In some aspects, one or more of jaws 124 a-e comprisessteel. In some aspects, one or more of jaws 124 a-e is anodized. In someaspects, one or more of jaws 124 a-e comprises an inert material such ashard rubber and/or plastic. In some aspects, jaws 124 a-e are configuredto support a material system, such as a panel, from about 15° and about30° relative to a first wall 130 and/or second wall 132, which reducesliquid collection on a material system during corrosion testingperformed in apparatus 100. In some aspects, jaw 124 a is configured togrip a material system at a first end of the material system and jaw 124b is configured to grip the material system at a second end of thematerial system. In some aspects, jaws 124 a-e are configured to flex amaterial system simultaneously or alternatively.

A motor 126 operates jaws 124 a-e. Inlet tube 128 is coupled with motor126 at a first end and coupled with first wall 130 at a second end forproviding cooling material, such as air, to motor 126. Outlet tube 134is coupled with motor 126 at a first end and coupled with first wall 130at a second end for removing hot air exhaust from motor 126. Outerenclosure 136 surrounds motor 126 to enclose and protect the motor fromliquid emitted from fog nozzle 102 or any other liquid present inside ofapparatus 100. Jaws 124 a-e are supported by plate 146. Plate 146 issupported by legs 148 a, 148 b, 148 c, 148 d, 148 e, and 148 f. Legs 148a-f are coupled with plate 146 at a first end and a chamber wall, a rack150 a, or a rack 150 b at a second end. Parts of apparatus 100 describedherein may comprise materials that are suitably inert to conditionswithin apparatus 100 during a cyclic flexing fog spray process. Suitablyinert materials may include plastic, glass, stone, metal, rubber, and/orepoxy.

Apparatus 100 may be controlled by a processor based system controllersuch as controller 138. For example, the controller 138 may beconfigured to control apparatus 100 parts and processing parametersassociated with a cyclic flexing fog spray process. The controller 138includes a programmable central processing unit (CPU) 140 that isoperable with a memory 142 and a mass storage device, an input controlunit, and a display unit (not shown), such as power supplies, clocks,cache, input/output (I/O) circuits, and the like, coupled to the variouscomponents of the apparatus 100 to facilitate control of a cyclicflexing fog spray process. Controller 138 may be in electroniccommunication with, for example, outlet tube 134, vent 122, heater 120,and/or jaws 124 a-e.

To facilitate control of the apparatus 100 described above, the CPU 140may be one of any form of general purpose computer processor that can beused in an industrial setting, such as a programmable logic controller(PLC), for controlling various chambers and sub-processors. The memory142 is coupled to the CPU 140 and the memory 142 is non-transitory andmay be one or more of readily available memory such as random accessmemory (RAM), read only memory (ROM), floppy disk drive, hard disk, orany other form of digital storage, local or remote. Support circuits 144are coupled to the CPU 140 for supporting the processor in aconventional manner. Information obtained from cyclic flexing fog sprayprocesses with apparatus 100 may be stored in the memory 142, typicallyas a software routine. The software routine may also be stored and/orexecuted by a second CPU (not shown) that is remotely located from thehardware being controlled by the CPU 140. The memory 142 is in the formof computer-readable storage media that contains instructions, that whenexecuted by the CPU 140, facilitates the operation of the apparatus 100.The instructions in the memory 142 are in the form of a program productsuch as a program that implements the method of the present disclosure.The program code may conform to any one of a number of differentprogramming languages. In some aspects, the disclosure may beimplemented as a program product stored on computer-readable storagemedia for use with a computer system. The program(s) of the programproduct define functions of the aspects (including the methods describedherein). Illustrative computer-readable storage media include, but arenot limited to: (i) non-writable storage media (e.g., read-only memorydevices within a computer such as CD-ROM disks readable by a CD-ROMdrive, flash memory, ROM chips or any type of solid-state non-volatilesemiconductor memory) on which information is permanently stored; and(ii) writable storage media (e.g., floppy disks within a diskette driveor hard-disk drive or any type of solid-state random-accesssemiconductor memory) on which alterable information is stored. Suchcomputer-readable storage media, when carrying computer-readableinstructions that direct the functions of the methods and apparatusdescribed herein, are aspects of the present disclosure.

FIG. 3 is a plan view of an apparatus 300 for accelerating andcontrolling the corrosion-related failure modes of a material system,according to an aspect of the disclosure. As shown in FIG. 3, thecomponents of apparatus 300 are the same as the components shown inapparatus 100 of FIG. 1, except that motor 126 is not encompassed byouter enclosure 136 (outer enclosure 136 is not present), motor 126 islocated external to first chamber wall 130, and inlet tube 128, andoutlet tube 134 are not present. Motor 126 is coupled to first chamberwall 130. In some aspects, motor 126 (coupled to first chamber wall 130)translates bending motion inside the chamber via a screw, such as a ballscrew, Acme screws, Lead screws, Roller screws, and screw mount, or anaxle, passing into the chamber (not shown). A screw maintains spacingbetween stationary block 406 and mobile block 404 during flexing.

FIG. 4 is a perspective view of a flexer 400 configured to performcyclic flexing, according to an aspect of the disclosure. Flexer 400 maybe located inside of a material performance chamber, as described forFIG. 1. As shown in FIG. 4, flexer 400 includes a mobile block 404 and astationary block 406. Stationary block 406 is mounted to plate 146 bymounting bolts 410 a and 410 b. Mobile block 404 is slidably disposed onplate 146 adjacent to stationary block 406. Linear displacement betweenstationary block 406 and mobile block 404 is maintained by guide rods408 a and 408 b. Guide rods 408 a and 408 b may comprise stainlesssteel, high density polypropylene, high density polyethylene, chromium,such as an Armology coating, and combinations thereof. Each of guiderods 408 a and 408 b is coupled with stationary block 406 and mobileblock 404. Guide rods 408 a and 408 b are parallel to one another.Stationary block 406 and mobile block 404 mount or otherwise supportjaws 124 a-f. Stationary block 406 mounts a first side of jaws 124 a-fin a stationary position during flexing, while mobile block 404 mounts asecond side of jaws 124 a-f and allows movement of the second side ofjaws 124 a-f during flexing. Stationary block 406 and mobile block 404may comprise high density polyethylene. During flexing, the mobile blockis shifted laterally relative to the stationary block from a startingpoint to an end point resulting in flexing of the material systempositioned in jaws 124 a-f. The starting point, end point, and shiftdistance may be controlled by a user of flexer 400 based on test fixturemechanical boundary limits, mechanical stop blocks, or fixture drivingsystem software controls. Each of stationary block 406 and mobile block404 includes a base and a plurality of stanchions extending from thebase perpendicular thereto. Each stanchion may be rectangular or angledto provide an angle on which each of the jaws 124 a-f can be mounted.Jaws 124 a-f are hinged, which allows bending of a material system whilecompressing the material system. For example, jaws 124 a-f may bemounted on one side of each stanchion and disposed at an angle from, forexample, 15° to 30° relative to a line perpendicular to the base. Otherangles relative to perpendicular are contemplated to achieve a desiredtesting condition for a material panel. The angle of jaws 124 a-fdetermines the angular position of the material system. In some aspects,a material system is disposed at an angle from, for example, 15° to 30°relative to a line perpendicular to the base. In some aspects, jaws 124a-f are non-conductive and non-metallic so as to have little or nogalvanic effect on the material system. One or more of jaws 124 a-f maycomprise high density polyethylene, commercial grade Titanium (II) withpolyethylene insert, sacrificial 316SS with polyethylene insert, orcombinations thereof, which prevents (partially or completely) galvaniccorrosion of the jaws and material systems during testing. One or moreof jaws 124 a-f may comprise a sleeve cover comprising, for example,polyethylene, which further prevents galvanic corrosion of the jaws andmaterial systems during testing. In some aspects of the presentdisclosure, a material performance chamber contains more than one flexer400. In some aspects where a material performance chamber contains morethan one flexer 400, guide rods 408 a and 408 b extend through multipleflexers 400.

A flexer, such as flexer 400, provides variable displacement of a mobileblock and material systems at variable frequencies that are adjustablein real-time. A flexer also allows for application of tension andcompression to a material system.

A material testing process such as a cyclic flexing fog spray process,for example, within apparatus 100, may be performed by exposing amaterial system, such as a panel, to a treating liquid, such as a saltfog, and flexing the material system. The exposing may be performed forfrom about 1 hour to about 4500 hours, such as about 200 hours to about2000 hours, such as about 500 hours to about 1000 hours. Exposing amaterial system to a treating liquid for about 1 hour mimics, forexample, salt fog exposure experienced by the material system as part ofan aircraft in an arid climate. Exposing a material system to a treatingliquid for about 4500 hours mimics, for example, salt fog exposureexperienced by the material system as part of an aircraft in a veryhumid climate or a moderately humid climate for a prolonged period oftime. The liquid may contain water that is reagent grade water. Theliquid may be a salt solution. The salt solution may comprise sodiumchloride. The salt solution may contain about 2 parts sodium chloride in98 parts water to about 6 parts sodium chloride in 94 parts water, suchas about 5 parts sodium chloride in about 95 parts water. The liquid,such as a salt solution, may contain less than about 0.1% of bromide,fluoride and iodide. The liquid, such as a salt solution, may containless than about 1 ppm, such as about 0.3 ppm, by mass of copper. Theliquid, such as a salt solution, might not contain anti-caking agents,as such agents may act as corrosion inhibitors. Material systems whichmay be tested include, for example, aircraft panels which may form theskins or fuselage of an aircraft, a coated lap joint between two metalpanels, a wing-to-fuselage assembly, and combinations thereof. Thematerial systems may comprise a metal or alloy. Common material systemsmay comprise aluminum. Panels may comprise aluminum and/or an alloy,such as AA2024, AA7075, AA5083, aluminum lithium, or high entropymulticomponent alloys. The liquid may be atomized to form the treatingliquid, such as a salt fog, that may have a pH ranging from about 3 toabout 11, such as about 5 to about 8, such as about 6.5 to about 7.2. pHmay be measured using a suitable glass pH-sensing electrode, referenceelectrode, and pH meter system. It may be desirable to adjust the pH ofthe treating liquid. For example, a treating liquid having a low pH maymimic a polluted atmosphere containing acid rain and the like.Furthermore, pH of the liquid that is atomized into the treating liquidmay be adjusted to recalibrate the liquid during an exposing process. pHmay be adjusted by, for example, addition of hydrochloric acid (HCl) todecrease the pH or addition of sodium hydroxide (NaOH) to increase thepH. The liquid, such as a salt fog, may be flowed at a rate of about 0.5milliliters per hour (mL/h) to about 5 mL/h per 80 cm² of horizontalcollection area, such as about 1 mL/h to about 2 mL/h per 80 cm² ofhorizontal collection area. In some aspects, a material system, such asa panel, may be flexed by a fixture support using one of jaws 124 a-e orby a plurality of jaws 124 a-e. Flexing may be performed at varyingfrequencies to mimic the effect of mechanical stresses for corrosiveconditions experienced by an aircraft material system under real worldconditions. For example, a material system may be flexed at a frequencyfrom about 0.1 Hertz (Hz) to about 150 Hz, about 0.1 Hz to about 100 Hz,about 0.1 Hz to about 60 Hz. Furthermore, the greater the curvature of aflexed material system, the greater the degradation to the materialsystem using apparatus and methods of the present disclosure. Forexample, a flat panel having a length of 6 inches may be gripped by twojaws with a distance of 6 inches between the two jaws. The panel may beflexed at a rate of 0.33 Hz during exposure to a salt fog solution. Inanother example, a flat panel having a length of 7.5 inches may begripped by two jaws also having a distance of 6 inches between the twojaws. The panel may be flexed at a rate of 0.33 Hz during exposure to asalt fog solution. The panel having a length of 7.5 inches has anincreased curvature and undergoes increased degradation as compared tothe panel having a length of 6 inches under otherwise identicalconditions. Without being bound by theory, mechanical stresses that givecurvature to a material system result in cracking of the material systemwhich permits access of corrosive fluid, such as a salt fog, into acrack of the material system. After entering a crack of the materialsystem, corrosive fluid may further enter between various additionallayers, if present, on the surface of the material system. Additionallayers may include, for example, a surface finish, a primer, and/or atop coat. Accordingly, corrosive fluid may cause corrosion of thematerial system and/or one or more of the additional layers of thematerial system. Such conditions mimic the conditions experienced by anaircraft material system, such as a panel, during real world use.

In some aspects, an exposure zone, such as an enclosure 160 of apparatus100, may be maintained at a temperature ranging from about −196° C. toabout 100° C., −50° C. to about 95° C., 0° C. to about 50° C., such asabout 33° C. to about 37° C., for example about 35° C., during theexposing of a material system to a treating liquid (such as a saltsolution atomized into a salt fog), and/or the flexing the materialsystem. The temperature may be monitored by a recording device or by athermometer (not shown) that can be read from an outside surface ofapparatus 100. In some aspects, exposing a material system, such as apanel, to a liquid, such as a salt fog, and flexing the material systemmay be performed concurrently. In some aspects, exposing a materialsystem, such as a panel, to a liquid, such as a salt fog, and flexingthe material system may be performed sequentially. In some aspects, amaterial system may be exposed to a salt fog and flexed concurrently aswell as sequentially, which provides recreation of an irregular orvariable flight-specific strain profile that may be experienced by amaterial system in service. In some aspects, exposing a material systemto a liquid and/or flexing the material system may be interrupted toinspect, rearrange, or remove the material system, and/or replenish asolution, such as a solution in liquid reservoir 104.

Once the exposing process is complete, the extent of corrosion ismeasured. The material system is washed, such as with water, to removebyproducts of the treating solution, e.g., salt deposits, from thesurface of the material system, followed by drying of the materialsystem. A material system may, additionally or alternatively, be washedwith an HCl solution and/or hexamethylene tetramine, followed by rinsingwith reagent grade water. After washing, the material system may bedried. The extent of corrosion may be determined by a mass losstechnique by weighing the material system after washing/drying andsubtracting the weight from the weight of the material system before theexposing to a liquid, such as a salt fog, and the flexing.

A material system, such as a panel, may have one or more surface layerssuch as a surface finish, a primer, and/or a top coat. Corrosion mayoccur at one or more of these layers in a real world setting due tomechanical and chemical stresses. Apparatus and methods described hereinallow for corrosion testing that mimics the corrosion experienced by amaterial system under real world conditions by subjecting the materialsystem to mechanical as well as chemical stresses. Apparatus and methodsdescribed herein allow for corrosion testing at one or more of amaterial system surface, a finished surface, a primer surface, and/or atop coat surface.

Example 1

An aluminum panel measuring 3.75 inches wide by 14.5 inches long wassecured by two jaws in a fixture support in the device described inFIG. 1. While flexing the panel at about 1 Hz, the panel was exposed toa sodium chloride salt fog (pH 6.8) for 500 hours. After the exposingand flexing, the aluminum panel was washed with water and dried. Todetermine the overall corrosion of the panel under these conditions, thepanel was then weighed, and this weight was subtracted from the weightof the panel prior to exposing and flexing. Further, electrochemicalmeasurements were made on the material system to assess degree andextent of corrosive damage imparted during the test.

In some aspects, a material system is a flat metal panel, which may becoated. The material performance of the flat panel is tested bycyclically flexing the panel while exposing the panel to at least acycle of salt fog. Following exposure and flexing, the panel is assessedfor corrosion onset, rate of propagation, and performance.

In some aspects, a material system comprises two flat metal panelsconnected, joined, or fastened together using metallic fasteners,screws, bolts, or other hardware, before being exposed to at least acycle of salt fog. The material system may then be assessed forcorrosion onset, rate of propagation, and performance.

In some aspects, a material system comprises a mechanical joint orknuckle joint that may be made of metallic or composite materials andcoated before being exposed to a cyclic salt fog before being assessedfor corrosion onset, rate of propagation, and performance.

In some aspects, a material system comprises a structural systemreplicative of aircraft components, representing a side-of-body join, astringer-to-fuselage assembly, a fuselage panel, or wingspar-to-fuselage assembly. The produced assemblies may be actuated orflexed while being exposed to at least a cycles of salt fog before beingassessed for corrosion onset, rate of propagation, and performance.

Apparatus and methods described herein provide a controlled salt fogenvironment and monitoring of material performance, such as corrosion,on a variety of material systems, such as aircraft material systems,such as panels, coated lap joints between two or more panels,wing-to-fuselage assemblies, and combinations thereof. Apparatus andmethods described herein provide an ability to replicate in-service,real-world failure modes and mechanisms in a controlled exposureenvironment.

Mechanical flexing of a material system in an apparatus of the presentdisclosure may result in increased corrosion of a material system, suchas a panel. The compounding effects of mechanical and chemical stressescombine to induce corrosion, which more accurately replicates corrosionexperienced by a material system, such as an aircraft panel, in areal-world environment. Accordingly, the methods and apparatus of thepresent disclosure more accurately simulate the corrosion observed withaircraft material systems during real-world use of the aircraft. Methodsand apparatus of the present disclosure allow for testing corrosion ofstand-alone material systems and the interfaces between coating layers,which more accurately represents the corrosion experienced by materialsystems, such as panels, during actual use of the material systems aspart of an aircraft. The methods and apparatus of the present disclosurefurther allow re-creation of irregular flight-specific strain profilesso that improved predictive as well as forensic investigations ofaircraft material systems may be performed.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the present disclosure may be devisedwithout departing from the basic scope thereof. Furthermore, while theforegoing is directed to material systems, such as aircraft materialsystems, such as panels, coated lap joints between two or more panels,and wing-to-fuselage assemblies, aspects of the present disclosure maybe directed to other material systems not associated with an aircraft,such as a multicomponent material system used in aerospace, automotive,marine, energy industry, and the like.

What is claimed is:
 1. A method for determining material performancecomprising: exposing a material system to salt fog; and flexing thematerial system.
 2. The method of claim 1, wherein the flexing isperformed at a frequency from about 0.1 Hz to about 60 Hz.
 3. The methodof claim 1, wherein the flexing the material system and the exposing thematerial system are performed concurrently.
 4. The method of claim 1,wherein the flexing the material system and the exposing the materialsystem are performed sequentially.
 5. A method for determining materialperformance comprising: exposing a material system to a salt fog whereinthe pH of the salt fog ranges from about 3.0 to about 9.0; and flexingthe material system at a frequency from about 0.1 Hz to about 60 Hz. 6.The method of claim 5, wherein the flexing is performed by a jaw coupledwith the material system and a motor coupled with the jaw.
 7. The methodof claim 5, further comprising maintaining an exposure zone at atemperature of from about −50° C. to about 95° C. during the exposingthe material system to salt fog.
 8. The method of claim 5, wherein theexposing the material system and the flexing the material system areperformed in the same chamber.
 9. The method of claim 8, wherein theexposing the material system and the flexing the material system areperformed concurrently.
 10. A material performance chamber comprising: asalt fog chamber; and a jaw configured to flex a material system. 11.The material performance chamber of claim 11, further comprising: amotor located internal to the chamber; an inlet tube coupled with themotor at a first end and a first wall at a second end; and an outlettube coupled with the motor at a first end and the first wall or asecond wall at a second end.
 12. The material performance chamber ofclaim 11, further comprising a motor located external to the chamber.13. The material performance chamber of claim 12, wherein the motorcomprises an outer enclosure to protect the motor from a salt fog. 14.The material performance chamber of claim 11, further comprising: acontroller in electrical communication with a vent, a heater, and thejaw.
 15. The material performance chamber of claim 11, wherein the jawcomprises a material selected from the group consisting of high densitypolyethylene, high density polypropylene, commercial grade Titanium (II)with polyethylene insert, sacrificial 316SS with polyethylene insert,and combinations thereof.
 16. The material performance chamber of claim11, wherein the jaw comprises a sleeve cover, wherein the sleeve covercomprises polyethylene.
 17. The material performance chamber of claim11, wherein the jaw is non-conductive and non-metallic.
 18. The materialperformance chamber of claim 11, further comprising a mobile block and astationary block.
 19. The material performance chamber of claim 19,further comprising a first guide rod and a second guide rod.
 20. Thematerial performance chamber of claim 11, wherein the jaw is disposed atan angle from about 15° to about 30° relative to a line perpendicular tothe base.